Decrement or a variable.
x--; // decrement x by one and returns the old value of x
--x; // decrement x by one and returns the new value of x
x:
an integer or long (possibly unsigned)
The original or newly decremented value of the variable.
x = 3;
y = --x; // x and y both contain 2
x = 3;
y = x--; // y still contains 3, while x contains 2